As this type of ink supply device, there has been known an ink supply device where a plurality of ink transfer rollers which are divided in the lengthwise direction of an ink fountain roller which constitutes an ink fountain are arranged adjacent to the ink fountain roller, the respective ink transfer rollers are individually changed over between a transfer position where the ink transfer roller is brought into contact with the ink fountain roller and a non-transfer position where the ink transfer roller is disposed away from the ink fountain roller, and using a control device, ink is transferred by changing over the position of the predetermined ink transfer roller for every transfer timing at predetermined intervals, and a rotational angle of the ink fountain roller from a position where the ink transfer roller is brought into contact with the ink fountain roller to a position where the ink transfer roller is separated from the ink fountain roller is controlled for every ink transfer roller thus controlling a circumferential length of ink transferred to the ink transfer roller from the ink fountain roller (Patent Literature 1 and Patent Literature 2). The above-mentioned control of the rotational angle of the ink fountain roller is performed by controlling a time from a point of time that an instruction of switching the ink transfer roller to a transfer position is outputted to a point of time that an instruction of switching the ink transfer roller to a non-transfer position is outputted.
In such a device, ink ejected to a surface of the ink fountain roller from the inside of the ink fountain is transferred to the ink transfer roller during a period where the ink transfer roller is changed over to the transfer position, and ink transferred to each ink transfer roller is transferred to the ink distribution roller during a period of time that the ink transfer roller is changed over to a non-transfer position. Then, by controlling a circumferential length of ink transferred for every ink transfer roller, a quantity of ink supplied to the ink distribution roller, that is, to a printing surface is controlled for every ink transfer roller.
The reason that a quantity of ink is controlled for every ink transfer roller is that an optimum quantity of ink differs corresponding to the position in the widthwise direction depending on a pattern of a printed matter. That is, a quantity of ink with respect to each ink transfer roller is set corresponding to a pattern area ratio of the printed matter.
A target value of a quantity of ink is expressed by percentage as a “graph value” for every color and for every ink transfer roller, and based on “graph value” which is preliminarily set corresponding to a pattern area ratio of a printed matter, a circumferential length of ink transferred to the ink transfer roller from the ink fountain roller (to be more specific, an ON/OFF time of a switching valve which moves each ink transfer roller) is controlled.
In the above-mentioned ink supply device, when color change is performed at the time of exchanging an original plate, by performing cleaning of the original plate and, thereafter, by supplying ink corresponding to a pattern area after the exchange of the original plate, proper printing can be performed. When a color change is not performed at the time of exchanging an original plate, cleaning may be performed or may not be performed. At the time of performing exchanging of an original plate without accompanying a color change, in both of the case where cleaning of the original plate is performed and the case where cleaning of the original plate is not performed, printing is performed by supplying ink corresponding to a pattern area after the exchange of the original plate.